Known methods of developing electrostatic, latent images fall into one of two categories:
1) Liquid Development in which toner is deposited from a suspension of toner particles in an insulating liquid. This liquid is normally a volatile organic compound which wets the surface of a charge bearing member, thereby producing a film of the organic compound. A portion of the film is transferred together with the toner image to the paper or substrate and then it normally evaporates into the atmosphere.
2) Dry Development in which toner is applied in a powder form. The toner is normally fixed to the paper or substrate by heating the toner or substrate. The range of particle size for the toner is such that airborne particles of the toner create an environmental hazard.
Other prior systems include U.S. Pat. No. 3,486,922 to Cassier et al. which discloses a water based toner with a continuous hydrophobic surface, an external electrical field and limited contact time during development. Such a thin continuous layer of hydrophobic toner powder which is spread on the surface of water can produce a satisfactory toner image on the member carrying an electrostatic latent charge pattern. However, it is difficult to consistently produce a thin uniform, continuous toner layer on the water. Therefore, such a system is highly unreliable.
Prior art development in transfer electrophotography has been carried on mainly by means of dry toners. The use of dry toners requires fusing the dry toner image which requires a considerable amount of heat. Further, when water was used it would discharge the charge on the charge bearing element because it is conductive.